Flying of model aircraft, such as model airplanes, is a popular hobby enjoyed by thousands of individuals around the country. Since most people who enjoy flying model aircraft do not have a sufficient amount of open land on their own property, they often go to flying fields that are shared by many other individuals.
On a typical day, twenty or more individuals may share space at a flying field to fly their model aircraft. The aircraft are typically controlled by separate remote control systems including a receiver mounted in the aircraft and a base transmitter unit having one or more flying controls thereon. Under the rules promulgated by the FCC and adopted by the AMA (Academy of Model Aeronautics), all remote control systems for model aircraft must operate on rf energy over a frequency range of 72.01-72.99 MHz. This frequency range is broken down into fifty channels, each being spaced at 20 kHz increments. Thus, there are a limited number of channels available to individuals who wish to fly model aircraft. This has presented a problem in the past, especially when more than one of the flying enthusiasts at a common flying site attempts to operate their model aircraft at the same time and on the same channel. If this condition should arise, mutual interference over the common channel will cause a loss of control over the model aircraft being flown on PG,3 the common channel. Often, the mutual interference will cause all of the affected model aircraft to crash.
Attempts to control this problem in the past have been made by flying clubs and by the owners of the common flying sites by establishing a "rule" that once a available channel is selected, a frequency flag must be taken to serve as a warning to all others that the channel corresponding to the frequency flag is no longer available. Despite these attempts, many accidents continue to occur due to interference.